During the last several years there has been an explosion of new knowledge concerning normal and neoplastic hematopoiesis. Modern immunology, molecular biology, virology, endocrinology and cell biology have impacted on the field of hematopoiesis in a manner that has led to startling scientific advances. Hematopoietic systems have been used as the key models to investigate the regulation of mammalian gene expression. The establishment of human leukemic cell lines has provided critical tools for studying cell differentiation and the production and response to hematopoietic hormones and lymphokines. Human T lymphocyte cell lines have facilitated the definition of a virus which appears to be the best candidate virus causing human neoplasia. Similarly, hematopoietic systems have been used extensively to define the relationship between abnormal cytogenetics and neoplasia. New technology now permits the in vitro study of thrombopoiesis and lymphopoiesis and in vivo methods have been productively applied to the exciting area of gene transfer in intact animals. The Conference on Normal and Neoplastic Hematopoiesis brought together the best scientists working in these areas to present their latest data and to exchange new information at a critical time with regard to recent progress in the field. The conference emphasized recent developments in molecular biology, virology, immunology and cell biology as they relate to normal and malignant hematopoiesis and the neoplastic state in general. The clinical implications of new findings in this area are substantial and they were covered in the final session.